The present invention relates to a silicone rubber composition or, more particularly, to a silicone rubber composition capable of giving a cured rubbery elastomer having excellent resistance against fatigue caused by repeated stretching or bending, which is an essential characteristic property of rubbers used in dynamic applications such as rubber contacts in keyboard instruments, cover boots of isochronous joint in automobiles, diaphragms, tubes for medical pumps and the like. The invention also relates to a cured silicone rubber article obtained by curing the above mentioned silicone rubber composition.
As is well known, silicone rubbers in general have excellent physical properties such as high electric insulation, heat and cold resistance, weatherability, low permanent compression set, rubbery elasticity and the like along with chemical and physiological inertness so that they are useful in a wide field of applications including electric and electronic instruments, business machines, automobiles, aircrafts, food processing and medical instruments, hobby goods and so on. These applications include not only static applications but also dynamic applications in which the rubber-made parts receive repeated mechanical action such as stretching, bending, vibration and the like as is typical in the rubber-made parts used as rubber contacts of keyboard, cover boots of an iso-chronous joint of automobiles, diaphragms and tubes in medical pumps and the like.
Silicone rubbers in general, however, are not quite satisfactory as a rubbery material used in the above mentioned dynamic applications in respect of their relatively low resistance against fatigue by repeated stretching and bending so that it is eagerly desired to improve the dynamic stability of silicone rubbers. It is known that the dynamic fatigue performance of synthetic rubbers can be improved by several means for uniform distribution of crosslinks, low crosslinking density, low elastic modulus, decreased loading and uniform dispersion of fillers, elimination of coarse particles from the filler and so on. These prior art methods, however, are not quite effective for silicone rubbers. For example, the test value of silicone rubbers obtained by using a conventional de Mattia fatigue testing machine can rarely exceed one million cycles in respect of the fatigue resistance against stretching and bending even by undertaking the above mentioned means for improvement having effectiveness in ordinary synthetic rubbers. Accordingly, one of the important problems in the technology of silicone rubbers is to improve the dynamic fatigue performance thereof without affecting the generally excellent physical and chemical properties of silicone rubbers.